The numbers in 6mm and 6.5 millimeter cartridge names say how wide the bullet is, not what the case looks like. That is where most mistakes start.

1. Treating all 6mm cartridges as one

The 6mm Remington, the 6mm Creedmoor and the 6mm ARC all fire a 6mm bullet from entirely different cases, and none can be fired in a rifle chambered for another. The 6mm Remington is at 6mm remington ammo. The 6mm Creedmoor is at 6mm creedmoor ammo for sale.

The 6mm ARC, with its 80-grain loads, is at 6mm arc 80 grain ammo.

2. Shopping by bullet diameter alone

A search for 6.5 ammunition covers a dozen cartridges. A rifle marked 6.5 Creedmoor, whose Federal loads are at federal 6.5 creedmoor ammo, will not take a 6.5 PRC or a 6.5x55.

3. Putting 6.5 Grendel in an ordinary AR-15

The Grendel needs its own barrel, bolt and magazines, even though it uses the same lower receiver as a 5.56 rifle. Its loads are at 6.5 grendel ammo for sale.

4. Assuming the 6.5 PRC fits a Creedmoor rifle

The 6.5 PRC is a longer cartridge, and a rifle or magazine sized for the Creedmoor may not take it. Check the maker's chambering before you buy a box of 6.5 prc ammo.

5. Ignoring recoil and barrel life in a magnum

The 6.5-300 Weatherby is a belted magnum that burns a lot of powder, so it kicks harder and wears barrels faster than a Creedmoor. It is a fine cartridge for long shots, but it is not a casual plinker, and its loads are at 6.5-300 weatherby magnum ammunition.

6. Using a match bullet on game

A hollow-point match bullet is built for accuracy, not for opening reliably on an animal. The 6.5x55 hollow-point loads, at 6.5x55 hollow point ammo, are usually match loads, and a hunter should choose a soft-point or bonded bullet instead.

7. Trusting an old rifle's bore

Surplus rifles such as those chambered for the 6.5 Carcano vary in bore size, and ammunition that suits one rifle may group poorly in another. Have a gunsmith check the bore before you order, and read the soft-point loads at 6.5 carcano soft point ammo with that in mind.

8. Overlooking twist rate

Heavier bullets need faster twists. A 100-grain 6mm bullet, such as the 6mm XC loads at 6mm xc 100 grain ammo, generally wants a faster barrel twist than the light varmint bullets many older 6mm rifles were built for. Check the twist rate of your barrel before you buy.

General guidance only. Never fire a cartridge in a rifle that is not marked for it, and confirm the chambering, current stock and state shipping restrictions before ordering.